Electrophotography is a useful process for printing images on a receiver (or “imaging substrate”), such as a piece or sheet of paper or another planar medium (e.g., glass, fabric, metal, or other objects) as will be described below. In this process, an electrostatic latent image is formed on a photoreceptor by uniformly charging the photoreceptor and then discharging selected areas of the uniform charge to yield an electrostatic charge pattern corresponding to the desired image (i.e., a “latent image”).
After the latent image is formed, charged toner particles are brought into the vicinity of the photoreceptor and are attracted to the latent image to develop the latent image into a toner image. Note that the toner image may not be visible to the naked eye depending on the composition of the toner particles (e.g., clear toner).
After the latent image is developed into a toner image on the photoreceptor, a suitable receiver is brought into juxtaposition with the toner image. A suitable electric field is applied to transfer the toner particles of the toner image to the receiver to form the desired print image on the receiver. The imaging process is typically repeated many times with reusable photoreceptors.
The receiver is then removed from its operative association with the photoreceptor and subjected to heat or pressure to permanently fix (i.e., “fuse”) the print image to the receiver. Plural print images (e.g., separation images of different colors) can be overlaid on the receiver before fusing to form a multicolor print image on the receiver.
One problem that can occur in electrophotographic printing systems is that cross-track spacing variations can occur for various components. Such cross-track spacing variations are sometimes called “skew.” For example, the spacing between the charging subsystem and the surface of the photoreceptor can vary across the cross-track width of the photoreceptor. This can produce a gradient in the charge on the photoreceptor produced by the charging system, which can in turn produce non-uniformities in the printed images. Other subsystems such as the exposure subsystem and development subsystem can also be susceptible to image quality variations due to cross-track spacing variations. Such cross-track spacing variations can be difficult to detect and correct. For example, if a cross-track density gradation is detected in a uniform region of a printed image is observed, it can be difficult to troubleshoot which subsystem may have a cross-track spacing variation that is causing the artifact. This is particularly true for systems that are deployed at a customer location where specialized equipment may be unavailable.
There remains a need for a method to reliably troubleshoot and characterize cross-track spacing variations in an electrophotographic printing system that can be performed without the need for specialized equipment.